-add range(a,b), accept if (input >= a AND input <= b)
-add operators rep(in) = rep(in,0,-1), rep1(in) = rep(in,1,-1) and opt(in) = rep(0,1)
- add '~>' and '<~' operators.
From https://github.com/scala/scala/blob/v2.10.2/src/library/scala/util/parsing/combinator/Parsers.scala#L1 :
'<~' is a parser combinator for sequential composition which keeps only the left result.
-add phrase parser
-add not and guard parsers